Amphiuma red cells enlarge and regulate their volume by utilizing in amiloride-sensitive Na transport mechanism. Cl is not essential to this transport process unlike the comparable response in duck erythrocytes. The Amphiuma transport process acts as a Na/H antiport or alternatively as a Na/OH symport. As such it is capable of transferring the energy inherent in a cation (Na) electrochemical gradient maintained across a membrane to an electrochemical gradient involving H ions.